When you estimate sums and differences, you can use the same methods you would use for whole numbers.
Examples
For easier adding, round each number to the nearest ten:
70.7 -> 70 + 78.5 -> + 80
Clustering
Month
Hours Worked
May
72.50
June
68.50
July
69.75
August
71.75
As you can see, the addends are clustered around the number 70. So that is the number we use in the problem.
70
70
70 +70
280 Front-end estimation 3.6 +5.9
8
Here is a short video.
For more examples, go to here
Other kinds of Estimation
One of the many other kinds of estimation there is out there is called front-end estimation. When using front-end estimation, you add or subtract the first digits. Then, repeat the step in the next value positions.
Also, there is something else called clustering . Clustering is another form of estimation that you use when all of the addends are close to the same number.
When you estimate sums and differences, you can use the same methods you would use for whole numbers.
Examples
For easier adding, round each number to the nearest ten:
70.7 -> 70
+ 78.5 -> + 80
Clustering
70
70
70
+70
280
Front-end estimation
3.6
+5.9
8
Here is a short video.
For more examples, go to here
Other kinds of Estimation
One of the many other kinds of estimation there is out there is called front-end estimation. When using front-end estimation, you add or subtract the first digits. Then, repeat the step in the next value positions.
Also, there is something else called clustering . Clustering is another form of estimation that you use when all of the addends are close to the same number.
Links:
http://www.teachertube.com/index.php
http://www.glencoe.com/sec/math/prealg/mathnet/pr01/pdf/0502a.pdf
http://www.algebra-online.com/estimating-sums-differences-mixed-numbers-1.htm